Gt Goku is equal to majin buu at base and his ssj is supposedly 100x stronger as opposed to 50x, his ssj3 should likewise be proportionately better and yet at this stage baby Vegeta easily overwhelmed him. Ssj4 was a match for Oozaru baby Vegeta who was 10x stronger than Baby Vegeta making ssj4 more than 10x stronger than ssj3.
SSJG allowed Goku to fight on good terms with Bills who previously put Goku down with a finger, the last time we saw a feat like this was tao vs Blue. Since Blue was gokus equal at that point and we know the result of the original goku vs tao it seems like Bills feat can be mimmicked so long as one has at least twice as much power as you do. In other words does not warrant Bills being 1000x stronger than goku which is a fourth as strong as ssj4 goku should be